Thermoplastic materials include those materials that can be repeatedly melted and cooled to a solid. Thermoplastic material includes waxes and thermoplastic adhesives, also referred to as “hot melt” adhesives, etc. “Hot melt” adhesives are used in a wide variety of applications including the assembly of various types of products including furniture, doors, windows, etc., and the closing of boxes, containers, etc.
Typically, solid hot melt adhesive, in various shapes and sizes, is supplied to a melter that includes a heated tank and/or a heated grid to produce molten hot melt adhesive. Solid hot melt adhesive can also be supplied in drums or barrels in which the adhesive is melted by the use of a platen. After heating, the molten adhesive is pumped through a heated hose, to maintain the molten material at the required application temperature, to an applicator or dispenser, sometimes referred to as a dispensing “gun” or gun, or a gun module, comprising a valve and a nozzle. Heated hoses are believed to be a primary source of charring problems associated with hot melt adhesives, particularly in systems requiring relatively low melt rates. In such applications, the residence time of the molten adhesive within a heated hose can exceed the “pot life” of the adhesive as a result of the relatively high volume of molten adhesive within the hose and the relatively low usage rate. “Pot life” as used herein is the maximum time at the system temperature before the adhesive starts to degrade resulting in increased viscosity and charring. Oversized tanks or other reservoirs of molten adhesive can also contribute to this problem. Exceeding the “pot life” of a thermoplastic adhesive may result in operational problems, such as filter clogging, and the cleaning required after charring has occurred.
It is desirable to provide an adhesive dispensing system that reduces charring. It may also be desirable to provide an adhesive dispensing system where the time the material is maintained at elevated temperature is significantly reduced and/or the volume of material is reduced. Finally, it may also be desirable to eliminate the need of heated hoses for transporting liquefied hot melt.